This application is a national stage of PCT/DE99/03795 filed Nov. 27, 1999 and based upon German national application 19900936.8 of Jan. 13, 1999 under the International Convention.
The invention relates to an injector for applying fluids, particularly contrast media for X-ray and nuclear spin tomography, with a tube system consisting of connecting tubes and a pump tube and with a plurality of storage vessels each connected via a connection tube as well as a branching piece to the pump tube leading to a cannula.
In injectors known in practice several storage vessels are mounted on a frame of the injector and together can deliver a volume sufficient for the examination of a number of patients during a work day or a work shift, without requiring frequent interruptions during which the fluid has to be replaced the storage vessel has to be exchanged. This exchange process in itself is relatively cumbersome, since the storage vessel to be replaced has to be detached from the connection tube and, as a result air enters the connection tube and forms there an air bubble. The same problem also arises when the vessel runs empty during examinations, thereby allowing air to enter the connection tube, air which is not allowed to reach the patient and be injected into a vein, since this creates the risk of embolisms.
It is therefore the object of the invention to provide an injector of the kind mentioned in the introduction so that the penetration of bubbles in the pump tube will be safely avoided at each operation stage, particularly also during the replacement of the storage vessels.
According to the invention the foregoing object is accomplished in an injector of the aforementioned kind in that to each connection tube a gas bubble detector as well as a valve are assigned and in that to the pump tube a pumping organ is assigned, which reverses the flow of fluid from the storage vessel to the cannula.
This injector has the advantage that the penetration of an air bubble into the connection tube, for instance when a storage vessel runs dry, is detected, after which by means of the valve assigned to the connection tube containing the air bubble, the connection tube is blocked and another connection tube can be turned open by means of its valve, so that the examination of the patient can continue without delay. Besides with the injector of the invention it is possible not only to detect the presence of the air bubble in the connection tube, but furthermore, after the replacement of the empty storage vessel with a full one, the pumping organ makes it possible to reopen the previously closed valve and to exert a pressure surge on the liquid existing in the pump tube and the connection tube which displaces the liquid upstream, whereby the air bubble is pushed back from the connection piece into the new storage vessel where it can rise to the surface, so that as a result the connection tube is continuously filled with liquid and the exchanged storage vessel can be used.
Within the framework of the invention it is further provided that the pump tube be associated with a roller pump for the active transport of the fluid from the storage vessel to the cannula. This has the advantage that gravity need not be relied upon to inject the fluid into the patient against the vein pressure, whereby furthermore the amount of fluid injected per given time unit can be varied by changing the rotary speed of the roller pump. The use of a roller pump has the particular advantage that no direct contact takes place between the fluid inside the pump tube and the roller pump, the sterility of the fluid being thus safeguarded at all times, and also ensuring that there is no danger of fluid contamination.
It has proven to be suitable when the gas bubble detector is formed by an ultrasound sender and receiver, by means of whose signals the associated valve can be switched. A gas bubble detector built in this way has sufficient precision and definition capability and delivers electric signals which can be used by conventional signal processing in order to switch the assigned valve.
Suitably the valves are formed by tube clips which narrow down the cross section of the connection tubes to the extent that no liquid can pass the same. The tube clips seizing the connection tubes from the outside have the advantages already mentioned in connection with the roller pump, that the sterility of the fluid is safeguarded at all times, since no components contact the fluid itself in order to interrupt the flow.
Within the framework of the invention it is provided that the tube clips have a prop pressing the connection tube against an abutment, thereby narrowing the cross section. The use of a prop for obstructing the fluid flow is more favorable than the use of a tube collar which can also be used in principle, but can not be readjusted so quickly and is subjected to higher wear.
For better monitoring of the injection process the tube clips have a switch detecting the position of the prop.
Further according to a particularly preferred embodiment within the framework of the invention, the pumping organ is provided with a correcting element adjacent to the pump tube, by means of which the pump tube can be deformed and the liquid existing inside the tube upstream of the correcting element can be pressed upstream. Again any direct contact with the fluid is avoided, since the pumping organ engages only the outside of the pump tube. Another advantage of this embodiment of the pumping organ consists in the simplicity of its mechanical construction, in the low cost of manufacture and its operational reliability. Due to the construction of the pumping organ it is also insured that the reversal of the fluid flow in the pump tube can be only short-term, i.e. no negative pressure can be generated in the tube system, which would exert an extended suction on the vein of the patient. The short-term pressure impulse created by the pumping organ is however sufficient for the minimal displacement of the upstream fluid column to the point that the air bubble which entered the connection tube is again removed from the same. Naturally, by accepting higher costs for the apparatus, it is also possible to assign a pumping organ to each connection tube instead of the pump tube.
The pumping organ has a particularly simple construction when the correcting element is formed by a unilaterally fastened W-shaped spring whose flank at the free end can be displaced from a rest position inclined with respect to the pump tube into a position running parallel with the pump tube and pressed against the pump tube. In this design of the correcting element, when the same is actuated the pump tube is at first deformed point by point and the fluid flow is stopped downstream, whereby during the subsequent pressing of the free flank the liquid upstream of the locked point is pressed in the direction of the storage vessel.
In principle it is possible to displace the freely hanging pump tube by means of the correcting element, until no further bending is possible and the clamping effect takes over. However it is better when on the side of the pump tube opposite to the correcting element a plate is arranged as an abutment, way the wear of the pump tube can then be reduced.
A two-arm lever can be provided for the adjustment of the correcting element. One arm of the lever in rest position can rest against the flank at the free end of the spring and its other arm can be coupled with a servo motor for the displacement of the correcting element.
A pressure chamber can be integrated in the tube system which is connected through at least one opening in the tube wall with the interior of the pump tube and can be filled with the fluid, and when the pressure chamber has a component which is adjustable under the effect of the fluid pressure and acts upon a pressure sensor. By monitoring the pressure in the tube system it is possible to determine how much fluid is actually being injected to the patient. Furthermore the pressure measurement represents a further safety device since, as a rule, disturbances during operation take effect always in the pressure existing in the tube system, for instance when due to a failure of the valves all connection tubes are closed and the pressure falls in the tube system, or when by using an unacceptable cannula whose cross section is too small the counterpressure increases excessively and therefore the pressure in the tube system also increases. Also leaks in the tube system are detected through a drop in pressure.
Since the pump tube to be used in combination with the roller pump has to be sufficiently elastic in order to convey the flow of fluid from the storage vessel to the cannula, which elasticity has a negative effect on the pressure measurement, between two segments of the pump tube a rigid pipe can be inserted, the rigid pipe having the opening to which the pressure chamber is attached.
In order to prevent a direct contact between the fluid and the pressure sensor, it is possible to simply use a fluid-proof, elastic membrane as the adjustable component.
Alternately it is possible to design the adjustable component as a piston tightened against the pressure chamber wall, which acts directly on the pressure sensor.
Since due to the pumping organ the fluid existing in the tube system is pushed upstream, at the downstream end of the tube system a suction is created. In order to securely prevent the patient""s blood from entering the tube system, and to avoid replacing the entire tube system when the patient changes, so that absolute hygiene is insured, it is provided to make the pump tube of two parts, the part forming the free end having at least one check valve. In this embodiment it is insured that only the patient tube itself has to be replaced, while the rest of the tube system remains free of contamination, as has been proven during a hygiene check.